no ROYAL SOCIETY OF CANADA 



Also it may be remarked that the supposed tail mark may in some 

 eases, if not in most, be due to the belly dragging along the mud or 

 sand, on which the impressions have been made. The exactness with 

 which the "tail" mark iisually runs along the middle of the space be- 

 tween the foot-marks appears to point to such an origin. And this ig 

 noticeable even where the track is curved, and where one might expect 

 the tail mark to sweep toward the outer side of the curve. In the case of 

 one track this "tail'' mark was found strongly marked on the crests of 

 the ridges of a Carboniferous ripple-marked layer, and yet the sand wa& 

 so firm that no footprints were preserved. 



In the scheme given in the following list the basis of arrangement 

 is the number of toes, as shown by the prints on the layers of the rock, 

 and as a subordinate character the weight and strength of the impres- 

 sion. 



Sir William Dawson has used the form of the impression as a basis 

 of classification and divides these footmarks into Hylopus (="digiti- 

 grade"), and Sauropus (=" plantigrade"). In this way he has associated 

 together footmarks' of a type which other writers have separated. His 

 classification brings togettier the prints of animals that had five toes and 

 (though with a question mark) others that had three, into one genus. 

 Also, it brings together under Sauropus, 8. unguifer in which the tracks 

 are near the usual chirotherian pattern, and 8. 8ydnensis, a species 

 which had an elephantine tread. 



E . Butts is also broad in his' use of his genus Notolacerta, which 

 contains digitigrade prints, with five toes on each foot, and planti- 

 grade prints with five toes on the hind foot and four on the front. 



Apart from the fact that 0. C. Marsh noticed and indicated by sev- 

 eral generic names the variations in the form of the footprints described 

 by him, the chief cause of the diversity of genera in the Paleozoic foot- 

 prints is that each author has described only one or a few prints, and 

 each has given new generic names. It is to reduce this redundancy of 

 names to something like method and order, that the author has under- 

 taken to present the following list, in which the footmarks are divided 

 into related groups with leading generic names. 



This arrangement is only to be considered tentative, and is 

 arbitrary in that one character, namely the number of toe marks of 

 the hind and fore feet is chiefly relied on for classifying. The 

 arrangement is also incomplete, in that the author has not sufficient 

 information of some species that have been described, to place them 

 in the series. And, furthermore, it should also be stated that no 

 attempt has been made to classify with these Batrachian tracks, others 

 that may have been described from the Palaeozoic deposits of Europe. 



